Relatively hard materials are often processed for mining and construction. The variety of materials include rock, concrete, asphalt, coal, and a variety of other types of mineral-based materials. A number of different methods for reducing the size of these hard materials have been developed. One traditional material size reduction method has been to drill relatively small holes in the material which are then packed with an explosive that is ignited, resulting in a rapid and cost effective method of size reduction. However, there are a variety of disadvantages to this technique, including the inherent risk of injuries, the production of undesirable noise, vibrations, and dust, and the fact that this process is difficult to utilize in situations where space is limited or where there is a potential risk of causing other gases to ignite.
Due to the above-described disadvantages associated with blasting techniques, alternative methods have been developed for reducing large surface areas of relatively hard materials. One alternative has been the use of reducing machines having rotary reducing components that move rigid and specialized reducing elements through paths of travel. The reducing components can include rotating drums that move the reducing elements through circular paths of travel. Such drums are typically attached to corresponding machines with a mechanism that allows the position and orientation of the drum to be controlled, to bring the reducing elements into contact with the material being reduced. Alternative reducing components can include boom-mounted chains that carry reducing elements. The chains are typically driven/rotated about their corresponding booms. The reducing elements are mounted to and move along the paths of travel defined by the chains. In use, the booms are moved (e. g., through a pivoting motion) to positions where the reducing elements are brought into contact with the material being reduced.
An example machine of the type described above is disclosed at U.S. Pat. No. 7,290,360. The disclosed machine is a surface excavation machine used for applications such as surface mining, demolishing roads, terrain leveling, and prepping sites for new construction or reconstruction by removing one or more layers of material. Surface excavation machines of this type provide an economical alternative to blasting and hammering and provide the advantage of generating a consistent output material after a single pass.
The reducing elements of reducing machines have been developed to withstand the impact loads and abrasion associated with material reduction activities. Reducing elements can be constructed in a variety of shapes and sizes and have been labeled with various terms including cutters, chisels, picks, teeth, etc. Typical reducing elements include leading impact points or edges and bases. The bases are constructed to fit into mounting structures that are integrated with drums or chains used to carry the reducing elements during material reducing applications. The harsh environment associated with material reducing applications virtually guarantees that the reducing elements will wear down over time.
Often, the tips or edges of the reducing elements have a harder construction (e.g., a solid carbide construction) than the bases of the reducing elements. When using new reducing elements to reduce material, the leading points or edges are exposed to the majority of the impacts and abrasion action. However, once the leading tips or edges becomes worn, the bases are exposed to more impacts and abrasive action. A variety of potential problems can arise when this occurs, including that the bases are less efficient at breaking the material, causing inefficient operation. Once reducing elements are worn there is also a risk of causing damage to the mounting structures of the drums or chains.
Several patent applications were filed in the 1970's, that describe replaceable bit holders. An early example is illustrated in U.S. RE28,310. Another example from that time frame is U.S. Pat. No. 4,068,897. There has been an on-going need for an improved replaceable bit holder, examples of the evolution of these holders can be seen in U.S. Pat. Nos. 4,621,871, 5,607,206, 6,619,756, and 6,854,810. These assemblies were developed for applications known at the relevant time, mainly for road milling or mining of relatively soft materials, such as coal. In about the 90's a new application started to develop for surface mining where this basic cutting structure started to be used for harder materials, including for mining iron ore.
There is now a need for an improved replaceable bit support. Recent efforts have been made to provide a better device, including those described in U.S. Patent Publication No. 2008/0093912, U.S. Patent Publication No. 2011/0266860, and U.S. Patent Publication No. 2011/0148179. These are all relatively wide structures, that attempt to provide the improved structural support to the bit. In surface mining the height of the cutting bit above the surface of the drum and the width of the bit and its supporting structure has been found to affect performance. There is an on-going need for a replaceable bit support that is taller and narrower than known alternatives.